Globular clusters can host intermediate mass black holes

May 31. () –

Simulations have revealed that sufficiently dense molecular clouds can give rise to very massive stars that evolve into intermediate mass black holes.

This is indicated by research led by astronomer Fujii Michiko, from the University of Tokyo, which has been published in the journal Science.

“Previous observations have suggested that some massive star clusters (globular clusters) host an intermediate mass black hole (IMBH),” explains it’s a statement Fujii on the motivation of the research project. “An IMBH is a black hole with a mass of 100-10,000 solar masses. Until now, there has been no solid theoretical evidence proving the existence of IMBH with 1,000-10,000 solar masses compared to the least massive (stellar mass) and the most massive (supermassive).”

Birth nests can evoke images of warmth and tranquility. Not so with the stars. Globular star clusters form in agitation. Density differences cause stars to collide and merge. As stars continue to merge and grow, gravitational forces grow with them. Repeated stellar collisions in the dense, central region of globular clusters are called runaway collisions.. They can lead to the birth of very massive stars with more than 1,000 solar masses.

These stars could potentially evolve into IMBH. However, previous simulations of already formed clusters suggested that stellar winds carry away most of their mass, leaving them too small. To investigate whether IMBHs could “survive,” the researchers needed to simulate a cluster while it was still forming.

“Star cluster formation simulations were challenging because of the cost of the simulation,” Fujii says. “For the first time, we successfully performed numerical simulations of the formation of globular clusters, modeling individual stars. By resolving individual stars with a realistic mass for each, we were able to reconstruct star collisions in a compact environment. For these simulations, we have developed a new simulation code, in which we were able to integrate millions of stars with great precision.

In the simulation, runaway collisions effectively led to the formation of very massive stars that evolved into intermediate-mass black holes. The researchers also found that the mass ratio between the cluster and the IMBH matched that of the observations that originally motivated the project.

“Our ultimate goal is to simulate entire galaxies by resolving individual stars” Fujii notes of future research. “It is still difficult to simulate Milky Way-sized galaxies by resolving individual stars using currently available supercomputers. However, it would be possible to simulate smaller galaxies, such as dwarf galaxies. We also want to target the first clusters, star clusters formed in the early universe. The first clusters are also places where IMBH can be born.”